In lithography, there is an ongoing desire to reduce the size of features in a lithographic pattern in order to increase the density of features on a given substrate area. In photolithography, the push for smaller features has resulted in the development of technologies such as immersion lithography and extreme ultraviolet (EUV) lithography, which are however rather costly.
A potentially less costly road to smaller features that has gained increasing interest is so-called imprint lithography (and in particular nano-imprint lithography), which generally involves the use of a “stamp” (often referred to as an imprint template) to transfer a pattern onto a substrate. An advantage of imprint lithography is that the resolution of the features is not limited by, for example, the emission wavelength of a radiation source or the numerical aperture of a projection system. Instead, the resolution is mainly limited to the pattern density on the imprint template.
Imprint lithography involves the patterning of an imprintable medium on a surface of a substrate to be patterned. The patterning may involve pressing a patterned surface of an imprint template onto a layer of imprintable medium, and/or vice versa, such that the imprintable medium flows into recesses in the patterned surface and is pushed aside by protrusions on the patterned surface. Pressing may not be required in some embodiments, where instead capillary forces may be sufficient to ensure that the imprintable medium flows into one or more recesses in the patterned surface and is pushed aside by one or more protrusions on the patterned surface. The recesses define pattern features of the patterned surface of the imprint template. Typically, the imprintable medium is flowable when the patterned surface and the imprintable medium are together. Following patterning of the imprintable medium, the imprintable medium is suitably brought into a non-flowable or frozen state and the patterned surface of the imprint template and the patterned imprintable medium are separated. The substrate and patterned imprintable medium are then typically processed further in order to pattern or further pattern the substrate. The imprintable medium is typically formed from resist droplets on the surface of a substrate to be patterned.